Per-worker integration of the service bus shipped in DEBT-029. Publishes
are fire-and-forget; subscribes wake polling loops. Bus stays optional —
if get_bus() fails or DECNET_BUS_ENABLED=false, workers log once and
continue in poll-only mode (mirrors decnet/mutator/engine.py:run_watch_loop).
- scripts/bus/smoke-mutator.sh: boots decnet bus, subscribes to
topology.>, publishes one event per mutation-lifecycle state plus
a topology.status transition, asserts all four land on the
subscriber. Cheap E2E for the topic hierarchy the mutator + SSE
route rely on.
- development/DEBT.md: mark DEBT-030 ✅ resolved (Phase A) with a
summary of what shipped; flag the optimistic staged-buffer editor
as Phase B follow-up, not debt.
Land the `decnet bus` worker and `get_bus()` factory. Transport is a
host-local UNIX-domain socket (0660, group=decnet); authz is the file
mode. Wire framing is a tiny verb-line + 4-byte-BE length + orjson body.
NATS-style wildcard topics (`*`, `>`). At-most-once, fire-and-forget —
DB stays the source of truth. `FakeBus` / `NullBus` for tests and the
disabled path. Cross-host federation is deferred to a future
`--bridge-tcp` mode; DEBT-030 is master-only and unblocked.
